Band engineered nano-crystal non-volatile memory device utilizing enhanced gate injection

ABSTRACT

Non-volatile memory devices and arrays are described that utilize reverse mode non-volatile memory cells that have band engineered gate-stacks and nano-crystal charge trapping in EEPROM and block erasable memory devices, such as Flash memory devices. Embodiments of the present invention allow a reverse mode gate-insulator stack memory cell that utilizes the control gate for programming and erasure through a band engineered crested tunnel barrier. Charge retention is enhanced by utilization of high work function nano-crystals in a non-conductive trapping layer and a high K dielectric charge blocking layer. The band-gap engineered gate-stack with symmetric or asymmetric crested barrier tunnel layers of the non-volatile memory cells of embodiments of the present invention allow for low voltage tunneling programming and erase with electrons and holes, while maintaining high charge blocking barriers and deep carrier trapping sites for good charge retention.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to integrated circuits and inparticular the present invention relates to non-volatile memory devices.

BACKGROUND OF THE INVENTION

Memory devices are typically provided as internal storage areas in thecomputer. The term memory identifies data storage that comes in the formof integrated circuit chips. There are several different types of memoryused in modern electronics, one common type is RAM (random-accessmemory). RAM is characteristically found in use as main memory in acomputer environment. RAM functions as a read and write memory; that is,you can both write data into RAM and read data from RAM. This is incontrast to read-only memory (ROM), which permits you only to read data.Most RAM is volatile, which means that it requires a steady flow ofelectricity to maintain its contents. As soon as the power is turnedoff, whatever data was in RAM is lost. Computers almost always contain asmall amount of ROM that holds instructions for starting up thecomputer.

EEPROM (electrically erasable programmable read-only memory) and Flashmemories are special types of non-volatile ROMs that can be written anderased. A Flash memory is a type of EEPROM that is typically erased andreprogrammed in blocks instead of a single bit or one byte (8 or 9 bits)at a time. Flash and EEPROM memories may use floating gate technology ortrapping technology non-volatile memory cells. Floating gate cellsinclude source and drain regions that are laterally spaced apart to forman intermediate channel region. The source and drain regions aretypically formed in a common horizontal plane of a silicon substrate.The floating gate, generally made of doped polysilicon, is disposed overthe channel region and is electrically isolated from the other cellelements by oxide. The non-volatile memory function for the floatinggate technology is created by the absence or presence of charge storedon the isolated floating gate. In floating node/embedded trapnon-volatile memory cells, the stored charge is “trapped” and stored ina non-conductive trapping layer. One example of this trapping technologythat functions as a non-volatile memory is thesilicon-oxide-nitride-oxide-silicon (SONOS) architecture. In the SONOSarchitecture, the nitride trap layer can capture and store electrons orholes in order to act as a non-volatile memory.

The memory cells of both an EEPROM memory array and a Flash memory arrayare typically arranged into either a “NOR” architecture (each celldirectly coupled to a bit line) or a “NAND” architecture (cells coupledinto “strings” of cells, such that each cell is coupled indirectly to abit line and requires activating the other cells of the string foraccess).

A problem in Flash/EEPROM floating gate and SONOS memory cell arrays isthat voltage scalability affects the minimum cell size, and consequentlythe overall memory density of any resulting array. Both SONOS andfloating gate Flash/EEPROM memories consume relatively high powercompared to other memory technologies, requiring external or on-chiphigh voltage/current supplies for programming and erase operations. Dueto the high programming voltage requirement, neighboring cells must beseparated sufficiently apart (significantly greater than the minimumfeature size) so as not to be disturbed by the capacitive couplingeffect during programming of the active cell. This problem is moresevere with scaling of the feature size capability, affecting celldensity. In addition, the high programming/erase voltages diminishdevice endurance and retention by damaging the materials of the memorycell and generating flaws. As integrated circuit processing techniquesimprove, manufacturers try to reduce the feature sizes of the devicesproduced and thus increase the density of the IC circuits and memoryarrays. Additionally, with progressive scaling of feature size,fundamental device leakage issues such as short-channel effects and gatedielectric leakage need to be contained in order to take advantage ofscaling.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art forlow power scalable non-volatile memory cell devices.

SUMMARY OF THE INVENTION

The above-mentioned problems with producing a non-volatile memory cellthat allows for increased device feature scaling with low voltageprogramming, efficient erasure, high charge retention, enhanced speedand reliability and other problems are addressed by the presentinvention and will be understood by reading and studying the followingspecification.

The present invention encompasses a band engineered reverse modenon-volatile memory cell that comprises a substrate that has a pluralityof implanted regions. These regions act as the drain and source of thecell.

A multiple layer tunnel dielectric is formed over a trap layer havinghigh work function nano-crystals embedded in it. The trap layer isformed over a charge blocking region that is formed over a substrate.The tunnel dielectric has asymmetric properties such that a first energylevel is required to move an electron from a control gate through thedielectric to the trapping layer. A second energy level is required tomove the electron from the trapping layer to the control gate. Thecomposition and/or quantity of layers of the tunnel dielectric determinethe first and second energy levels and, thus, the volatility of the celland the speed of charge trapping.

For one embodiment, the invention provides a reverse mode non-volatilememory cell comprising a first and second source/drain regions formed ina substrate coupled by a channel region, a charge blocking layer formedover the channel region, a trapping layer formed over the chargeblocking layer, wherein the trapping layer is a relatively trap-freedielectric, a plurality of nano-crystals embedded in the trapping layernear the charge blocking layer, a crested barrier tunnel insulator layercontaining two or more sub-layers formed over the trapping layer, and acontrol gate formed over the crested barrier tunnel layer.

Other embodiments are also described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an energy band diagram of a typical prior art SONOSstructure.

FIG. 2 shows an energy band diagram of the SONOS structure of FIG. 1under a bias condition.

FIGS. 3A-3D shows a memory cell and band diagrams of an embodiment ofthe present invention.

FIG. 4 shows a memory cell of another embodiment of the presentinvention.

FIG. 5 shows a memory cell band diagram of yet another embodiment of thepresent invention.

FIGS. 6A and 6B detail NOR and NAND architecture memory arrays inaccordance with embodiments of the present invention.

FIG. 7 details a system with a memory device in accordance withembodiments of the present invention.

FIG. 8 details a memory module in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The terms wafer and substrate used previously and inthe following description include any base semiconductor structure. Bothare to be understood as including bulk silicon, silicon-on-sapphire(SOS) technology, silicon-on-insulator (SOI) technology,silicon-on-nothing, thin film transistor (TFT) technology, doped andundoped semiconductors, epitaxial layers of silicon supported by a basesemiconductor, as well as other semiconductor structures well known toone skilled in the art. Furthermore, when reference is made to a waferor substrate in the following description, previous process steps mayhave been utilized to form regions/junctions in the base semiconductorstructure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present invention isdefined only by the claims and equivalents thereof.

Non-volatile memory devices and arrays, in accordance with embodimentsof the present invention, facilitate the utilization of reverse modenon-volatile memory cells that have band engineered gate-stacks andnano-crystal charge trapping in EEPROM and block erasable memorydevices, such as Flash memory devices. Embodiments of the presentinvention allow a reverse mode gate-insulator stack memory cell thatutilizes the control gate for programming and erasure through a bandengineered crested tunnel barrier. Charge retention is enhanced byutilization of high work function nano-crystals in a non-conductivetrapping layer and a high K dielectric charge blocking layer. Theband-gap engineered gate-stack with symmetric or asymmetric crestedbarrier tunnel layers of the non-volatile memory cells of embodiments ofthe present invention allow for low voltage tunneling programming anderase with electrons and holes, while maintaining high charge blockingbarriers and deep carrier trapping sites for good charge retention. Thedirect tunneling program and erase capability reduces damage to thegate-stack and the crystal lattice from high energy carriers, reducingwrite fatigue and leakage issues and enhancing device lifespan, whileallowing for memory cells that can take advantage of progressivelithographic and feature size scaling. Memory cell embodiments of thepresent invention also allow multiple levels of bit storage in a singlememory cell through incorporation of multiple trapped charge centroidsand/or multiple threshold voltage levels.

In normal mode SONOS or floating gate devices, the silicon substrate isactive as the source of electrons and holes during programming and eraseoperations. In contrast, the gate electrode serves as the source ofelectrons and holes during program and erase for the reverse modedevice. In the case of the normal mode device, during program/erasecycling injected hot carriers adversely affect the integrity of thesilicon/insulator interface as well as that of the tunnel insulatoritself. Consequently, device transconductance is degraded and endurance,retention and device reliability are reduced. Reverse mode devices areimmune to such adverse effects since the channel silicon/insulatorinterface is relatively passive during programming and erase operations,when charge injection/extraction is occurring at the control gate.Reverse mode devices, therefore, provide higher reliability, enhancedendurance, and other associated beneficial device characteristics.

FIG. 1 illustrates an energy band diagram of typical prior artsilicon-oxide-nitride-oxide layers of a SONOS structure at flatbands.Flatband conditions exist when no charge is present in the semiconductorso that the silicon energy band is flat. It is assumed that this occursat zero gate bias (neglecting the work-function difference between thegate electrode and silicon).

The illustrated structure is comprised of the silicon substrate 100, theoxide-nitride-oxide 101, 102, 103 (ONO) layer, and the control gate 104.The illustrated structure has an effective oxide thickness (EOT) of 12nm since the tunnel oxide has an EOT of 3.5 nm, the nitride trap 102 hasan EOT of 4.0 nm (physical thickness approximately 7.5 nm), and thecharge blocking oxide 103 has an EOT of 4.5 nm.

SONOS and nano-crystal types of non-volatile memory devices aretypically referred to as discrete trap or embedded trap devices. Thecharge to be stored in the trap layer 102 tunnels through the tunnelinsulator 101 and is confined there in trapping sites in the trappinglayer itself or in traps associated with nano-crystals due to the chargeblocking insulator layer 103. This charge trapping gate stack, with itselectrically isolated trapping layer, allows charge to be trapped nearthe channel region and affect the threshold voltage level of thenon-volatile memory cell. The tunneling may be accomplished by directand Fowler-Nordheim tunneling during write operations while holes tunnelby direct tunneling during erase operations. The trap layer 102 may benitride for SONOS or nano-crystals (silicon, germanium, or metalembedded oxides).

Stored charge retention and erase speed sensitivity can depend on thetunneling distance (i.e., tunnel insulator thickness). For example, anincrease in oxide insulator thickness from an EOT of 1 nm to 3 nm wouldresult in a charge retention increase of approximately five orders ofmagnitude but also reducing the erase speed by nearly the same amount.This is due to the fact that both the back-tunneling electron current aswell as the forward hole current are dependent on tunneling distancethat in turn depends on the insulator thickness, given the large bandenergy barriers (E_(b)) of oxide of 3.2 eV for electrons and 4.7 eV forholes (with reference to silicon), respectively. The tunnel oxide 101has an E_(b) of approximately 9 eV, the nitride layer 102 has an E_(b)of approximately 5.1 eV, and the charge blocking oxide has an E_(b) ofapproximately 9 eV.

The band diagram of FIG. 1 also shows that the Schottky barrier heightfor electrons (Φ_(b)) is 3.2 eV. Φ_(b) is the tunneling barrier forelectrical conduction across the interface and, therefore, is ofimportance to the successful operation of any semiconductor device. Themagnitude of Φ_(b) reflects the mismatch in the energy position of themajority carrier band edge of the silicon substrate 100 and the oxidetunnel insulator 101.

FIG. 2 illustrates an energy band diagram of the embodiment of FIG. 1that is under a bias condition of V on the gate 204. Under the appliedbias, the silicon-oxide interface barrier height, Φ_(b), does not changebut the tunneling distance is reduced as shown 203 for an oxidethickness of 3.5 nm (EOT=3.5 nm).

While SONOS or nano-crystal embedded trap memory cell devices showpromise in voltage scalability for non-volatile memory applications, aswell as somewhat higher programming speed/endurance when compared tofloating gate devices, these devices still exhibit characteristicallysmall values of logic window (Vt1−Vt0), have limited speed andreliability, and exhibit tunnel oxide degradation similar to floatinggate devices. This limits their application and potential andscalability in non-volatile memory. This is primarily due to the factthat the oxide thickness is required to be greater than 4 nm in order tomeet a 10 year retention requirement and that therefore a high field isstill required to transport charges through the tunnel oxide.

As such, issues with prior art floating gate, SONOS and embedded trapnon-volatile memory cells include, high programming voltage and powerrequirements, limited programming and erasure speed, limited devicescalability (without adversely affecting retention), and limited deviceendurance due to lattice damage from high energy carriers duringprogramming and erasure.

In embodiments of the present invention, the gate stack of thenon-volatile memory cell comprises a charge blocking dielectric layer, atrapping layer, a band engineered crested barrier tunnel layer, and acontrol gate forming a reverse mode memory cell field effect transistor(FET) device. The channel region is formed between two source/drainregions, the charge blocking dielectric layer is formed over thechannel, followed in turn by the trapping layer, the band engineeredcrested barrier tunnel layer, and the control gate. In this reverse modememory cell FET, charge storage and programming (writing and erasing) isaccomplished through the control gate to the trapping layer instead offrom the channel (as in a normal mode non-volatile memory cell),allowing the channel/charge blocking interface to remain relativelyunaffected by programming and erasure operations, increasing deviceendurance. The charge blocking region is formed of a dielectricinsulator material, which preferably is a high K dielectric so as toallow for reduction in overall stack EOT, and provides a high energybarrier and physical thickness to prevent electron and hole tunneling tothe channel and aid in charge retention. The trapping layer is formed oftrap-free high-K dielectric with high work function nano-crystals formednear the trapping layer/charge blocking layer interface, allowing amaximum electrostatic effect by the trapped charge on the channel for alarge logic window, while presenting a large physical tunnel distanceand barrier energy to the trapped charge prevent back-tunneling. Inalternative embodiment, the trapping layer is formed of bulk trapdielectric which may or may not have nano-crystals formed near thetrapping layer/charge blocking layer interface.

The tunnel layer in embodiments of the present invention comprisessuccessive layers of tunnel insulation of differing physical thicknessesand electron and hole tunnel barrier heights formed in a band-engineeredcrested barrier tunnel layer. In band-engineered crested barrier tunnellayers, the successive layers of tunnel insulation materials are chosensuch that a thin layer of high energy barrier material is combined withone or more lower barrier layers so that both an energy barrier and aphysical thickness are present to prevent carrier tunneling. Under anapplied field, the barriers of this crested tunnel layer distort toallow for low voltage carrier tunneling through the tunnel layer at highcarrier fluence through the combined effects of barrier lowering andthinning. This crested barrier tunnel layer, in combination with the lowEOT gate-insulator stack allows for high speed, low voltageprogramming/erasure of the memory cell. In one embodiment of the presentinvention, the tunnel barrier presents a symmetric barrier to bothelectron and hole tunneling. In another embodiment of the presentinvention, the tunnel barrier presents an asymmetric barrier to electronand hole tunneling, allowing for faster or slower programming orerasure. Band-engineered high K dielectric layers also provide enhancedprogramming speed at reduced field and carrier energy across the gateinsulator dielectric stack, enhancing endurance and reliability. Thecontrol gate can be formed of aluminum, tungsten, polysilicon or otherconductor material and is typically coupled to a word line or controlline.

FIG. 3A details a schematic cross section of a reverse-mode nano-crystaldevice 300 of an embodiment of the present invention. The gate-insulatorstack 304 of the non-volatile memory cell 300 comprises a chargeblocking dielectric layer 310, a trapping layer 312 with nano-crystals314 that are placed near the trapping layer/charge blocking layerinterface, a band engineered crested barrier tunnel layer 316 having twoor more sub-layers, and a control gate 318 forming a reverse mode memorycell field effect transistor (FET) device. The gate-insulator stack 304of the non-volatile memory cell 300 is formed over a channel region 302in a substrate between two source/drain regions 306, 308, the chargeblocking dielectric layer 310 is formed over the channel 302, followedin turn by the trapping layer 312, the band engineered crested barriertunnel layer 316, and the control gate 318. In this reverse mode memorycell FET, charge storage and programming (writing and erasing) isaccomplished from the control gate 318 through the crested tunnel layer316 to the trapping layer 312, allowing the channel/charge blockinginterface to remain relatively unaffected by programming and erasureoperations, increasing device endurance and reliability.

FIG. 3B details a flat band energy diagram 320 of one embodiment of thepresent invention. In FIG. 3B, the charge blocking layer 330 consists ofa 6 nm to 10 nm layer of HfSiON (K=17, band gap of 6.9 eV) formed over asilicon substrate/channel 322. A trapping layer 332 of 10 nm to 15 nm ofLa₂O₃ (K=30, bandgap of 4.3 eV) or HfAlO (K=17) is formed over thecharge blocking layer 330, having 4 nm nano-crystals 334 of platinum(Pt—NC) or germanium (Ge—NC) formed near the charge blocking/trappinglayer interface. A 3-layer “crested” tunnel dielectric 336 composed of a2.5 nm layer of HfSiON 340 (band gap of 6.9 eV) sandwiched between two1.25 nm layers of SiN 342 (band gap of 5.1 eV) is formed over thetrapping layer 332. As shown in FIG. 3B; at flat band with no biasvoltage applied the barrier energies of electrons and holes at theHfSiON 340 crest edge are 2.92 eV and 2.86 eV, respectively, and areapproximately symmetric, allowing an approximately equal applied voltagelevels and speed for both programming and erasure.

FIGS. 3C and 3D detail the energy band diagram 320 of the memory cellembodiment of FIG. 3B undergoing a programming operation 360 (FIG. 3D)and an erase operation 350 (FIG. 3C), respectively. As detailed in FIGS.3C and 3D, when either a negative gate voltage (−Vg for programming,FIG. 3D) or a positive gate voltage (+Vg for erasure, FIG. 3C) isapplied at the gate, the energy levels of the band diagram 320 aredistorted. This distortion of the band diagram has the effect oflowering the effective barrier energies of the tunnel barrier, while, atthe same time, the carriers gain energy, allowing them to overcome thelower energy barrier sub-layers of the crested tunnel barrier dielectric336. In addition, the applied gate voltage distorts the tunneldielectric's barrier energy “crest”, lowering the effective tunneldistance and enabling low energy tunneling through it. As both theeffective barrier energies (for electrons and holes) as well as theeffective tunnel distances are reduced and electron injection 360 orhole injection 350 occurs. It is noted that because of the crestedbarrier tunnel layer 336 and its barrier lowering and distortion underbias, this injection of carriers (both electrons and holes) from thecontrol gate are enhanced by many orders of magnitude over that of aconventional SONOS or embedded trap non-volatile memory cell.

In FIGS. 3C and 3D, once injected, the carriers get transported throughthe high K La₂O₃ trapping dielectric 332, which is relatively trap free,aided by the drift field across the layer. The carriers then get trappedat the La₂O₃/HfSiON interface where they are close to thesilicon/insulator interface by the virtual ground state of thenano-crystal trapping centers 334, which preferably have a highpotential well work function and a high placement density.

The high energy barriers for electrons and holes provided by the HfSiONcharge blocking layer 330 and the crested barrier tunnel layer 336,combined with the deep potential wells of the high work functionnano-crystals 334 helps prevent trapped-charge leakage to either thesubstrate or control gate 318, enhancing charge retention. The closeproximity of the trapped charges stored in the nano-crystals 334 to thesilicon/insulator interface of the channel 322, combined with the highdensity of trapping centers, result in large shift in device thresholdand a resulting large logic window.

The effective tunnel barrier 336 during programming or erasure of theembodiment of the present invention detailed in FIGS. 3B-3D is around ˜2ev, as compared to the energy barriers of 3.2 ev and 4.7 ev forelectrons and hole, respectively, for a Si0₂ tunnel dielectric in aconventional device. This lowers the required programming voltages andpower requirements of the resulting non-volatile memory cells. Thetunnel distance of the barrier is also reduced by the crested barrierdesign of the embodiment, thinning the tunnel distances and enhancingthe electron and hole carrier fluence by 6 to 8 orders of magnitude overthat of a conventional SONOS device. As a result, the programming anderasure speeds of memory cells of the present invention are bothenhanced by similar orders of magnitude.

The device detailed in FIGS. 3B-3D has a total physical gate insulatorstack thickness of less than 25 nm and yet has an overall EOT ofapproximately 5 nm due to the higher K value materials utilized in thegate-insulator stack layers. The tunnel layer 336 has an EOT of ˜1.87nm, which is approximately a third of the total stack EOT. The tunnellayer 336 therefore has a correspondingly initial applied voltage dropof the same proportion. The average peak field across the tunnel layer336 during a +/−5V programming or erase operation is less than or equalto 3.8 MV/cm, as compared to greater than 10 MV/cm field for aconventional Si0₂ tunnel dielectric. This lower peak field results in asignificant improvement in device power consumption, speed, enduranceand reliability. Furthermore, due to the barrier energy symmetry, thewrite speed (electron injection) and the erase speed (hole injection)are approximately the same. Whereas in Si0₂ the erase speed issignificantly slower than programming speed due to Si0₂ having a higherbarrier energy for holes than electrons. Charge tunneling to and fromsilicon substrate is also prevented during programming/erasure due tothe high barriers (of ˜3 eV) of the HfSiON charge blocking layer 330,the silicon substrate/HfSiON charge blocking layer 330 interface andchannel 322 remain relatively undamaged during the device lifetime.Device transconductance is thus preserved and leakage paths are notgenerated in the HfSiON charge blocking layer 330. The use of directtunneling and/or low voltage Enhanced Fowler-Nordheim tunneling forprogramming/erasure in embodiments of the present invention, combinedwith low leakage, provide significant operational power reductions. Theexpected device characteristics for the embodiment detailed in FIGS.3B-3D are: Programming Voltage: +/-5 Volts, Programming Speed<1μsec foreither write or erase, End-of-life Threshold Window: >2 Volts,Endurance >>1E10 cycles, and Retention >>10 years.

FIG. 4 details a non-volatile memory cell of another embodiment of thepresent invention having similar characteristics to the memory cell ofFIGS. 3B-3D that utilizes Hf-oxide based family of insulators. In FIG.4, the gate-insulator stack 404 consists of a HfSiON charge blockinglayer 410, HfAlO (Hafnium-Aluminum Oxide) or HfSiO_(x) (Hf-silicate)trapping layer 412 having high work function nano-crystals 414, such as,but not limited to, platinum nano-crystals (Pt-nc) or germaniumnano-crystals (Ge-nc), and a crested barrier tunnel layer 416 of layeredSiN/HfSiON/SiN insulator material. In addition, in FIG. 4, an injectorsilicon-rich nitride layer (I-SRN) 424 may optionally be incorporatedbetween the gate 418 and the tunnel layers 420, 422. The I-SRN layer 424locally enhances the field across the tunnel layer 416 and furtherenhances charge injection and device speed, enabling additional voltagescaling. An additional I-SRN layer can also be included at the tunnellayer/trapping layer interface. It is noted that that other higher Kdielectric materials could be used as the trapping layer dielectric 412in embodiments of the present invention, instead of, for example, La₂O₃(K=30, bandgap: 4.3 eV) to achieve similar device characteristics. Suchmaterials include, but not limited to, HfAlO (K=17), HfSiO_(x) (K=20),HfSiON (K=17, band gap of 6.9 eV), and LaAlO₃ (K=27.5, bandgap=6.5 eV).

FIG. 5 details a flat band energy diagram of a primarily Lanthanum-oxidefamily based non-volatile memory cell of yet another embodiment of thepresent invention designed to achieve additional voltage scaling. InFIG. 5, a gate-insulator stack having a crested barrier tunnel layer 516that is designed for hole injection for yet additional erase speedimprovement consists of a combination of 3 nm of Y₂O₃ (band gap: 5.6 eV,K=15) 520 and 2 nm of La₂O₃ (band gap: 4.3 eV, K=30) 522. The trappinglayer/nano-crystal dielectric medium 512 is also of 10 nm of La₂O₃. Thecharge blocking layer 510 comprises 8 nm of LaAlO₃ formed over a siliconsubstrate/channel 502. High work function nano-crystals 514 are embeddedat the interface of the charge blocking layer 510 and the trapping layer512. Due to the higher K values of the dielectric layers selected, forthe same physical thickness of layers as shown in FIGS. 3B-3D, the EOTof the insulator stack of FIG. 5 is around 3.5 nm, allowing theprogramming and erase voltage to be reduced to +/−3V while achievingsimilar device characteristics to the memory cell embodiment of FIGS.3B-3D. In addition, as stated above, the lower effective barrier forhole injection also further enhances erase speed in the embodiment ofFIG. 5.

For charge blocking layers of embodiments of the present invention, dueto lack of having to tunnel carriers through it for programming orerasure, the primary characteristics required for charge blocking layeris to provide a high enough barrier to electron or hole tunneling whileforming a saturated (no dangling bond) clean interface having a very lowdensity of states with the channel/silicon substrate. In order toeffectively prevent electron or hole tunneling, the barrier energy forboth should be greater than 2.5 eV and physical thicknesses greater thanor equal to 5 nm to prevent such injection during programming orerasure. Although Si0₂ fulfills most of the above-mentionedrequirements, it has a low K value (K=3.9) and higher K insulators aredesired for voltage scaling and the reduction of fixed charge formationat the interface. Examples of such higher K dielectric materialsinclude, but are not limited to HfSiON (K=17), HfAlO (K=17), La₂O₃(K=30, bandgap of 4.3 eV), LaAlO₃ (K=27.5, band gap: 6.5 eV),SiO_(x)C_(y) (Silicon-oxy-carbide: K=7, band gap: 6.3 eV), and HfSiO_(x)(Hafnium silicate: K=20, band gap 4.7 eV).

In yet another embodiment of the present invention, the charge blockinglayer consists of 5 nm or more of a high barrier, high K dielectricmaterial, a high density of platinum nano-crystals (with a densitygreater than or equal to 5E12/cm2) embedded in a trapping layer of 5nm-7 nm of Ta₂0₅ and a crested barrier tunnel layer. The crested barriertunnel layer formed of a 2 nm layer of Ta₂0₅ (K=26, band gap: 4.5 eV)formed over the 5 nm-7 nm nano-crystal embedded layer, a 10 nm-15 nmlayer of La₂O₃ (K=30, bandgap of 4.3 eV) and a thin overlayer ofinjector silicon-rich-nitride (I-SRN).

It is also noted that many combinations of dielectric layers to formcrested barriers are possible. In particular, those combining multiplehigh K layers. It should be noted however, for balancing retention withprogramming speed, the peak barrier height at flat band should be in theorder of 2 ev both for electrons and holes to avoid charge loss andretention issues through the tunnel layer, thereby limiting theselection of dielectric layers for tunneling medium. For example, layersof HfO₂ (K=24, band gap: 5.7 eV), TiO₂ (K=80, band gap: 3.5 eV), Ta₂O₅(K=26, band gap: 4.5 eV) can be combined with other layers such as SiN,Y₂O₃, or etc. to enhance electron injection, but such combination wouldcompromise retention. It should also be noted that tunneling layersshould preferably be those with reduced intrinsic trap density unlessselected to be extremely thin (direct tunneling).

It is noted that in embodiments of the present invention, trappingdielectric is preferred to be a high K dielectric with reduced trapdensity and that charge trapping occur mainly at the nano-crystallocations to promote well defined device characteristics. However, otherhigh K trapping dielectrics may also be considered such as, but notlimited to, TiO₂ (K=80), Ta₂O₅ (K=26), and AlN (K=10).

As previously stated, the two common types of EEPROM and Flash memoryarray architectures are the “NAND” and “NOR” architectures, so calledfor the similarity each basic memory cell configuration has to thecorresponding logic gate design. In the NOR array architecture, thefloating gate memory cells of the memory array are arranged in a matrixsimilar to RAM or ROM. The gates of each non-volatile memory cell of thearray matrix are coupled by rows to word select lines (word lines) andtheir drains are coupled to column bit lines. The source of eachnon-volatile memory cell is typically coupled to a common source line.The NOR architecture non-volatile memory array is accessed by a rowdecoder activating a row of non-volatile memory cells by selecting theword line coupled to their gates. The row of selected memory cells thenplace their stored data values on the column bit lines by flowing adiffering current from the coupled source line to the coupled column bitlines depending on their programmed states. A column page of bit linesis selected and sensed, and individual data words are selected from thesensed data words from the column page and communicated from the memory.It is noted that other memory arrays incorporating memory cellembodiments of the present invention are possible, including but notlimited to AND memory arrays and virtual ground memory arrays, and willbe apparent to those skilled in the art with the benefit of the presentdisclosure.

An EEPROM or Flash NAND array architecture also arranges its array ofnon-volatile memory cells in a matrix such that the gates of eachnon-volatile memory cell of the array are coupled by rows to word lines.However each memory cell is not directly coupled to a source line and acolumn bit line. Instead, the memory cells of the array are arrangedtogether in strings, typically of 8, 16, 32, or more each, where thememory cells in the string are coupled together in series, source todrain, between a common source line and a column bit line. This allows aNAND array architecture to have a higher memory cell density than acomparable NOR array, but with the cost of a generally slower accessrate and programming complexity.

A NAND architecture floating gate memory array is accessed by a rowdecoder activating a row of non-volatile memory cells by selecting theword select line coupled to their gates. In addition, the word linescoupled to the gates of the unselected memory cells of each string arealso driven. However, the unselected memory cells of each string aretypically driven by a higher gate voltage so as to operate them as passtransistors and allowing them to pass current in a manner that isunrestricted by their stored data values. Current then flows from thesource line to the column bit line through each floating gate memorycell of the series coupled string, restricted only by the memory cellsof each string that are selected to be read. This places the current orvoltage encoded stored data values of the row of selected memory cellson the column bit lines. A column page of bit lines is selected andsensed, and then individual data words are selected from the sensed datawords from the column page and communicated from the memory device.

FIG. 6A shows a simplified NOR non-volatile memory array 600 of a EEPROMor Flash memory device of an embodiment of the present invention. InFIG. 6A, a NOR array 600 couples non-volatile memory cells 602 ofembodiments of the present invention to bit lines 612, source lines 614,word lines 606, and a substrate connection 222. In forming the NOR array600, the bit lines 612 and source lines 614 are typically coupled to N+or P+ doped source/drain regions deposited in the substrate andseparated by a channel region. Each memory cell FET 602 has agate-insulator stack formed over the channel region and between thesource/drain regions of a bit line 612 and a source line 614, utilizingthe regions as a drain and source respectively (it is noted that thesource line 614 may be replaced with a second bit line 612 connection invirtual ground or multi-bit cell arrays, so that the current flowthrough the memory cell may be reversed). As described above, thegate-insulator stack is made of a charge blocking layer formed over thechannel region, a trapping layer with embedded nano-crystals formed onthe charge blocking layer, a composite band-gap engineered crestedbarrier tunnel layer formed on top of the trapping layer, and a controlgate 606 (typically formed integral to the word line 606, also known asa control gate line) formed over the tunnel layer. It is noted thatother NOR architecture memory array 600 configurations incorporatingembodiments of the present invention are possible and will be apparentto those skilled in the art with the benefit of the present disclosure.

FIG. 6B details a simplified NAND memory string 620 of a NANDarchitecture EEPROM or Flash memory device of an embodiment of thepresent invention. In FIG. 6B, a series of non-volatile memory cells 602of embodiments of the present invention are coupled together source todrain to form a NAND string 620 (typically of 8, 16, 32, or more cells).Each memory cell FET 602 has a gate-insulator stack made of a chargeblocking layer formed over the channel region, a trapping layer withembedded nano-crystals formed on the charge blocking layer, a compositeband-gap engineered crested barrier tunnel layer formed on top of thetrapping layer, and a control gate 606 (typically formed integral to theword line 606, also known as a control gate line) formed over the tunnellayer. N+ or P+ doped regions are formed between each gate insulatorstack to form the source and drain regions of the adjacent non-volatilememory cells, which additionally operate as connectors to couple thecells of the NAND string 620 together. Optional select gates 604, thatare coupled to gate select lines, are formed at either end of the NANDnon-volatile memory cell string 620 and selectively couple opposite endsof the NAND non-volatile memory cell string 620 to a bit line 612 and asource line 614. In a NAND memory array, the NAND architecture memorystring 620 of FIG. 6B would be coupled to bit lines 612, source lines614, word lines 606, and a substrate connection 622.

FIG. 7 shows a simplified diagram of a system 728 incorporating anon-volatile memory device 700 of the present invention coupled to ahost 702, which is typically a processing device or memory controller.In one embodiment of the present invention, the non-volatile memory 700is a NOR architecture Flash memory device or a NAND architecture Flashmemory device. The non-volatile memory device 700 has an interface 730that contains an address interface 704, control interface 706, and datainterface 708 that are each coupled to the processing device 702 toallow memory read and write accesses. It is noted that other memoryinterfaces 730 that can be utilized with embodiments of the presentinvention exist, such as a combined address/data bus, and will beapparent to those skilled in the art with the benefit of the presentdisclosure. In one embodiment of the present invention, the interface730 is a synchronous memory interface, such as a SDRAM or DDR-SDRAMinterface. Internal to the non-volatile memory device, an internalmemory controller 710 directs the internal operation; managing thenon-volatile memory array 712 and updating RAM control registers andnon-volatile erase block management registers 714. The RAM controlregisters and tables 714 are utilized by the internal memory controller710 during operation of the non-volatile memory device 700. Thenon-volatile memory array 712 contains a sequence of memory banks orsegments 716. Each bank 716 is organized logically into a series oferase blocks (not shown). Memory access addresses are received on theaddress interface 704 of the non-volatile memory device 700 and dividedinto a row and column address portions.

On a read access the row address is latched and decoded by row decodecircuit 720, which selects and activates a row/page (not shown) ofmemory cells across a selected memory bank. The bit values encoded inthe output of the selected row of memory cells are coupled to a localbit line (not shown) and a global bit line (not shown) and are detectedby sense amplifiers 722 associated with the memory bank. The columnaddress of the access is latched and decoded by the column decodecircuit 724. The output of the column decode circuit 724 selects thedesired column data from the internal data bus (not shown) that iscoupled to the outputs of the individual read sense amplifiers 722 andcouples them to an I/O buffer 726 for transfer from the memory device700 through the data interface 708.

On a write access the row decode circuit 720 selects the row page andcolumn decode circuit 724 selects write sense amplifiers 722. Datavalues to be written are coupled from the I/O buffer 726 via theinternal data bus to the write sense amplifiers 722 selected by thecolumn decode circuit 724 and written to the selected non-volatilememory cells (not shown) of the memory array 712. The written cells arethen reselected by the row and column decode circuits 720, 724 and senseamplifiers 722 so that they can be read to verify that the correctvalues have been programmed into the selected memory cells.

FIG. 8 is an illustration of an exemplary memory module 800. Memorymodule 800 is illustrated as a memory card, although the conceptsdiscussed with reference to memory module 800 are applicable to othertypes of removable or portable memory, e.g., USB flash drives, and areintended to be within the scope of “memory module” as used herein. Inaddition, although one example form factor is depicted in FIG. 8, theseconcepts are applicable to other form factors as well.

In some embodiments, memory module 800 will include a housing 805 (asdepicted) to enclose one or more memory devices 810, though such ahousing is not essential to all devices or device applications. At leastone memory device 810 is a non-volatile memory including memory cellcircuits of or adapted to perform methods of the present invention.Where present, the housing 805 includes one or more contacts 815 forcommunication with a host device. Examples of host devices includedigital cameras, digital recording and playback devices, PDAs, personalcomputers, memory card readers, interface hubs and the like. For someembodiments, the contacts 815 are in the form of a standardizedinterface. For example, with a USB flash drive, the contacts 815 mightbe in the form of a USB Type-A male connector. For some embodiments, thecontacts 815 are in the form of a semi-proprietary interface, such asmight be found on CompactFlash™ memory cards licensed by SanDiskCorporation, Memory Stick™ memory cards licensed by Sony Corporation, SDSecure Digital™ memory cards licensed by Toshiba Corporation and thelike. In general, however, contacts 815 provide an interface for passingcontrol, address and/or data signals between the memory module 800 and ahost having compatible receptors for the contacts 815.

The memory module 800 may optionally include additional circuitry 820which may be one or more integrated circuits and/or discrete components.For some embodiments, the additional circuitry 820 may include a memorycontroller for controlling access across multiple memory devices 810and/or for providing a translation layer between an external host and amemory device 810. For example, there may not be a one-to-onecorrespondence between the number of contacts 815 and a number of I/Oconnections to the one or more memory devices 810. Thus, a memorycontroller could selectively couple an I/O connection (not shown in FIG.8) of a memory device 810 to receive the appropriate signal at theappropriate I/O connection at the appropriate time or to provide theappropriate signal at the appropriate contact 815 at the appropriatetime. Similarly, the communication protocol between a host and thememory module 800 may be different than what is required for access of amemory device 810. A memory controller could then translate the commandsequences received from a host into the appropriate command sequences toachieve the desired access to the memory device 810; Such translationmay further include changes in signal voltage levels in addition tocommand sequences.

The additional circuitry 820 may further include functionality unrelatedto control of a memory device 810 such as logic functions as might beperformed by an ASIC (application specific integrated circuit). Also,the additional circuitry 820 may include circuitry to restrict read orwrite access to the memory module 800, such as password protection,biometrics or the like. The additional circuitry 820 may includecircuitry to indicate a status of the memory module 800. For example,the additional circuitry 820 may include functionality to determinewhether power is being supplied to the memory module 800 and whether thememory module 800 is currently being accessed, and to display anindication of its status, such as a solid light while powered and aflashing light while being accessed. The additional circuitry 820 mayfurther include passive devices, such as decoupling capacitors to helpregulate power requirements within the memory module 800.

It is noted that other memory cells, memory strings, arrays, and memorydevices in accordance with embodiments of the present invention arepossible and should be apparent to those skilled in the art with benefitof the present disclosure.

CONCLUSION

Non-volatile memory devices and arrays have been described that utilizereverse mode non-volatile memory cells that have band engineeredgate-stacks and nano-crystal charge trapping in EEPROM and blockerasable memory devices, such as Flash memory devices. Embodiments ofthe present invention allow a reverse mode gate-insulator stack memorycell that utilizes the control gate for programming and erasure througha band engineered crested tunnel barrier. Charge retention is enhancedby utilization of high work function nano-crystals in a non-conductivetrapping layer and a high K dielectric charge blocking layer. Theband-gap engineered gate-stack with symmetric or asymmetric crestedbarrier tunnel layers of the non-volatile memory cells of embodiments ofthe present invention allow for low voltage tunneling programming anderase with electrons and holes, while maintaining high charge blockingbarriers and deep carrier trapping sites for good charge retention. Thedirect tunneling program and erase capability reduces damage to thegate-stack and the crystal lattice from high energy carriers, reducingwrite fatigue and leakage issues and enhancing device lifespan, whileallowing for memory cells that can take advantage of progressivelithographic and feature size scaling. Memory cell embodiments of thepresent invention also allow multiple levels of bit storage in a singlememory cell through multiple charge centroids and/or multiple thresholdvoltage levels.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. This applicationis intended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

1. A reverse mode non-volatile memory cell, comprising: a first andsecond source/drain regions formed in a substrate coupled by a channelregion; a charge blocking layer formed over the channel region; atrapping layer formed over the charge blocking layer, wherein thetrapping layer is a relatively trap-free dielectric; a plurality ofnano-crystals embedded in the trapping layer near the charge blockinglayer; a crested barrier tunnel insulator layer containing two or moresub-layers formed over the trapping layer; and a control gate formedover the crested barrier tunnel layer.
 2. The reverse mode non-volatilememory cell of claim 1, wherein the two or more sub-layers of the tunnelinsulator layer comprise two or more sub-layers of dielectric material,where each sub-layer is has a barrier height greater than or equal to 2eV to both electrons and holes and where at least one sub-layer has abarrier height greater than 2 eV for electrons and/or holes.
 3. Thereverse mode non-volatile memory cell of claim 1, wherein an overallthickness of the tunnel insulator layer is greater than or equal to 5nm.
 4. The reverse mode non-volatile memory cell of claim 1, whereineach of the two or more sub-layers of the tunnel insulator layer are oneof HfSiON (Hafnium Silicon-Oxy-Nitride), HfAlO (Hafnium Aluminate),LaAlO₃ (Lanthanum Aluminate), SiO_(x)C_(y) (Silicon-oxy-carbide),HfSiO_(x) (Hafnium silicate), SiO₂ (silicon dioxide), La₂O₃ (LanthanumOxide), SiN (silicon nitride), Y₂O₃ (yttrium oxide), and HfO₂ (HafniumOxide).
 5. The reverse mode non-volatile memory cell of claim 1, whereinat least one layer of injector silicon-rich-nitride (I-SRN) is formedadjacent the tunnel insulator layer.
 6. The reverse mode non-volatilememory cell of claim 1, wherein the plurality of nano-crystals are deeppotential well/high work function nano-crystals.
 7. The reverse modenon-volatile memory cell of claim 1, wherein the plurality ofnano-crystals one of platinum and germanium nano-crystals.
 8. Thereverse mode non-volatile memory cell of claim 1, wherein the chargeblocking layer comprises a high K dielectric material having a barrierheight greater than or equal to 2 eV to both electrons and holes.
 9. Thereverse mode non-volatile memory cell of claim 1, wherein an overallthickness of the charge blocking layer is greater than or equal to 5 nm.10. The reverse mode non-volatile memory cell of claim 1, wherein thecharge blocking layer is one of HfSiON (Hafnium Silicon-Oxy-Nitride),HfAlO (Hafnium Aluminate), LaAlO₃ (Lanthanum Aluminate), SiO_(x)C_(y)(Silicon-oxy-carbide), HfSiO_(x) (Hafnium silicate), SiO₂ (silicondioxide), and La₂O₃ (Lanthanum Oxide).
 11. The reverse mode non-volatilememory cell of claim 1, wherein embedded nano-crystal trapping layer isone of HfSiON (Hafnium Silicon-Oxy-Nitride), HfAlO (Hafnium Aluminate),LaAlO₃ (Lanthanum Aluminate), HfSiO_(x) (Hafnium silicate), and La₂O₃(Lanthanum Oxide).
 12. A non-volatile memory device, comprising: anon-volatile memory array containing a plurality of reverse modenon-volatile memory cells formed into rows and columns, wherein one ormore of the plurality of reverse mode non-volatile memory cellscomprises, a first and second source/drain regions formed in a substratecoupled by a channel region, a charge blocking layer formed over thechannel region, a trapping layer formed over the charge blocking layer,wherein the trapping layer is a relatively trap-free dielectric, aplurality of nano-crystals embedded in the trapping layer near thecharge blocking layer, a crested barrier tunnel insulator layercontaining two or more sub-layers formed over the trapping layer; and acontrol gate formed over the crested barrier tunnel layer; a memoryinterface; and a control circuit coupled to the memory interface and thenon-volatile memory array.
 13. The non-volatile memory device of claim12, wherein the two or more sub-layers of the tunnel insulator layercomprise two or more sub-layers of dielectric material, where eachsub-layer is has a barrier height greater than or equal to 2 eV to bothelectrons and holes and where at least one sub-layer has a barrierheight greater than 2 eV for electrons and/or holes.
 14. Thenon-volatile memory device of claim 12, wherein an overall thickness ofthe tunnel insulator layer is greater than or equal to 5 nm.
 15. Thenon-volatile memory device of claim 12, wherein each of the two or moresub-layers of the tunnel insulator layer are one of HfSiON (HafniumSilicon-Oxy-Nitride), HfAlO (Hafnium Aluminate), LaAlO₃ (LanthanumAluminate), SiO_(x)C_(y) (Silicon-oxy-carbide), HfSiO_(x) (Hafniumsilicate), SiO₂ (silicon dioxide), La₂O₃ (Lanthanum Oxide), SiN (siliconnitride), Y₂O₃ (yttrium oxide), and HfO₂ (Hafnium Oxide).
 16. Thenon-volatile memory device of claim 12, wherein at least one layer ofinjector silicon-rich-nitride (I-SRN) is formed adjacent the tunnelinsulator layer.
 17. The non-volatile memory device of claim 12, whereinthe plurality of nano-crystals are deep potential well/high workfunction nano-crystals.
 18. The non-volatile memory device of claim 12,wherein the plurality of nano-crystals one of platinum and germaniumnano-crystals.
 19. The non-volatile memory device of claim 12 whereinthe charge blocking layer comprises a high K dielectric material havinga barrier height greater than or equal to 2 eV to both electrons andholes.
 20. The non-volatile memory device of claim 12, wherein anoverall thickness of the charge blocking layer is greater than or equalto 5 nm.
 21. The non-volatile memory device of claim 12, wherein thecharge blocking layer is one of HfSiON (Hafnium Silicon-Oxy-Nitride),HfAlO (Hafnium Aluminate), LaAlO₃ (Lanthanum Aluminate), SiO_(x)C_(y)(Silicon-oxy-carbide), HfSiO_(x) (Hafnium silicate), SiO₂ (silicondioxide), and La₂O₃ (Lanthanum Oxide).
 22. The non-volatile memorydevice of claim 12, wherein the trapping layer is one of HfSiON (HafniumSilicon-Oxy-Nitride), HfAlO (Hafnium Aluminate), LaAlO₃ (LanthanumAluminate), HfSiO_(x) (Hafnium silicate), and La₂O₃ (Lanthanum Oxide).23. The non-volatile memory device of claim 12, wherein the interface isa synchronous memory interface.
 24. The non-volatile memory device ofclaim 12, wherein the plurality of non-volatile memory cells of thememory array are further arranged into one of a NOR architecture memoryarray and a NAND architecture memory array.
 25. A system, comprising: ahost coupled to at least one non-volatile memory device, wherein the atleast one non-volatile memory device comprises, a non-volatile memoryarray containing a plurality of non-volatile memory cells formed intorows and columns, wherein one or more of the plurality of non-volatilememory cells comprises, a first and second source/drain regions formedin a substrate coupled by a channel region, a charge blocking layerformed over the channel region, a trapping layer formed over the chargeblocking layer, wherein the trapping layer is a relatively trap-freedielectric, a plurality of nano-crystals embedded in the trapping layernear the charge blocking layer, a crested barrier tunnel insulator layercontaining two or more sub-layers formed over the trapping layer, and acontrol gate formed over the crested barrier tunnel layer; a memoryinterface; and a control circuit coupled to the memory interface and thenon-volatile memory array.
 26. The system of claim 25, wherein the twoor more sub-layers of the tunnel insulator layer comprise two or moresub-layers of dielectric material, where each sub-layer is has a barrierheight greater than or equal to 2 eV to both electrons and holes andwhere at least one sub-layer has a barrier height greater than 2 eV forelectrons and/or holes.
 27. The system of claim 25, wherein an overallthickness of the tunnel insulator layer is greater than or equal to 5nm.
 28. The system of claim 25, wherein the plurality of nano-crystalsare deep potential well/high work function nano-crystals.
 29. The systemof claim 25, wherein the charge blocking layer comprises a high Kdielectric material having a barrier height greater than or equal to 2eV to both electrons and holes.
 30. The system of claim 25, wherein anoverall thickness of the charge blocking layer is greater than or equalto 5 nm.
 31. The system of claim 25, wherein the interface is asynchronous memory interface.
 32. The system of claim 25, wherein thehost is one of a processing device and memory controller.
 33. The systemof claim 25, wherein the plurality of non-volatile memory cells of thememory array are further arranged into one of a NOR architecture memoryarray and a NAND architecture memory array.
 34. A memory module,comprising: at least one NAND architecture memory device containing anarray with a plurality of non-volatile memory cells arranged in aplurality of memory blocks; a housing enclosing the at least one memorydevice; and a plurality of contacts configured to provide selectivecontact between the at least one memory device and a host system;wherein the at least one memory device contains an array having aplurality of non-volatile memory cells, one or more of the non-volatilememory cells comprising: a first and second source/drain regions formedin a substrate coupled by a channel region; a charge blocking layerformed over a channel region, a trapping layer formed over the chargeblocking layer, wherein the trapping layer is a relatively trap-freedielectric, a plurality of nano-crystals embedded in the trapping layernear the charge blocking layer, a crested barrier tunnel insulator layercontaining two or more sub-layers formed over the trapping layer, and acontrol gate formed over the crested barrier tunnel layer.
 35. Themodule of claim 34, further comprising a memory controller coupled tothe at least one memory device for controlling operation of each memorydevice in response to the host system.
 36. A memory module, comprising:a plurality of contacts; and two or more memory devices, each havingaccess lines selectively coupled to the plurality of contacts; whereinat least one of the memory devices comprises: a non-volatile memoryarray having a plurality of non-volatile memory cells, one or more ofthe non-volatile memory cells comprising, a first and secondsource/drain regions formed in a substrate coupled by a channel region;a charge blocking layer formed over a channel region, a trapping layerformed over the charge blocking layer, wherein the trapping layer is arelatively trap-free dielectric, a plurality of nano-crystals embeddedin the trapping layer near the charge blocking layer, a crested barriertunnel insulator layer containing two or more sub-layers formed over thetrapping layer, and a control gate formed over the crested barriertunnel layer.